1. Field of the Invention
This invention relates to apparatus and process for electroplating a plurality of pre-selected isolated areas on incremental segments of an elongate metal strip while maintaining the rest of the strip out of contact with the electroplating bath and providing for the controlled advancement of the strip as each segment is positioned for exposure to the electroplating bath.
2. The Prior Art
In many electroplating operations, e.g. operations wherein microcircuits are electroplated with gold, there is a need to minimize the amount of expensive metal utilized by closely restricting its deposition to only those surface areas where its presence is essential. It is desirable, however, that such selective deposition of the metal achieved without resorting to procedures which greatly restrict the production rate of an electroplating facility or to procedures which greatly increase the handling cost of the items being electroplated.
It has been known to use organic coatings to mask those areas of metallic substrates on which electroplating is not required and thereby avoid those areas being electroplated. After electroplating of such partially masked items is finished, the masking material is removed, leaving discrete electroplated zones. Such a process requires expensive coating and stripping steps. These steps add to the cost of the electroplating operation and also increase the probability that some of the costly work product will have to be scrapped because of damage incurred during the manufacturing operations.
The most suitable apparatus of the solution of such problems are disclosed in the commonly-owned and co-pending U.S. patent applications U.S. Ser. Nos. 90,632 and 95,995 filed by Kosowsky et al on Nov. 18, 1970 and Dec. 8, 1970, respectively. Such apparatus uses seal means to selectively isolate the surfaces of sheet which are to be exposed to contact with the electroplating fluid. The latter of these applications describes means to continuously electroplate an elongate suitable for use on very large runs of a strip with a particular metallic pattern; however, it has been found to be inconvenient to modify the sealing parts of such apparatus to accomodate a series of smaller runs on strips of different configurations. Another drawback to this continuous plating-type of apparatus is that it requires a relatively large amount of space because the various processing steps must be carried out as the strip moves through processing stations elongated to compensate for the movement of the strip. Therefore, it is desirable, for smaller orders and for providing apparatus that requires less space, to construct apparatus for the intermittent electroplating of elongate strips which will allow the strips to be advanced step-by-step and, consequently, to be stationary during the electroplating procedure.
Other suggestions have been made for accomplishing the electroplating of small selected areas, but these suggestions have been limited to small-scale, repair-type operations wherein the rigorous requirements of high-rate or continuous manufacture need not be considered. All of these prior suggestions are believed to be "batch-type" processes. For example, Ehrhart, in U.S. Pat. No. 3,071,521, discloses a single grommet-sealed chamber for use in repairing printed-circuits. Swanson, in U.S. Pat. No. 2,698,832, discloses a somewhat similar device utilizing a reservoir for an electroplating solution adapted to empty, by gravity flow, into a receptical for receiving the solution. Neither of these inventions has suggested a way whereby a large number of discrete areas can be carried out continuously at optimum current densities. Indeed, neither inventor, in solving his own particular problem has been faced with problems as complex as those involved in the elctroplating of a plurality of isolated areas on a continuously-advancing strip of substrate.
Ramirez et al, in U.S. Pat. No. 2,974,097, disclose means for continuously plating areas along the edges of a continuous strip. It should be noted, however, that the areas being electroplated are continuous areas running along the entire length of the strip, not a plurality of small areas on the faces of the strip. Thus, the problems of solution, distribution and isolation are much simpler than those encountered by the instant inventors.
All electrodeposited metals have crystalline structures which manifest themselves in the physical properties and appearance of the plated metal. In order to achieve plated deposits of suitable properties, it is necessary to control the current densities. Current densities which are too high will result in deposits of poor quality. Current densities which are too low will result in excessively long plating cycles and markedly reduce the production rate of the plating operations. A particular problem encountered in constructing apparatus which is suitable for continuous and simultaneous electroplating of a large number of selected areas is to assure maintenance of a suitable concentrated cation concentration at each of the discrete areas being plated. Without a suitable high concentration, it would be impossible to obtain a high quality plating in a desirable short time.
In commercial work, preparation of surfaces for plating is often as important as the electroplating step itself. This is especially so in electroplating surfaces for use in microcircuit components. Thus, special care should be exercised in the construction of apparatus to assure that the surfaces to be electroplated are processed with minimal contact by machine parts or by an operator's hands. This requirement has increased the difficulty of providing suitable apparatus for the electroplating of a large number of selected areas along a single, but extensive substrate.